Electronic device and magnetic device

ABSTRACT

A electronic device is disclosed having an underlying conductor formed in a predetermined pattern on a surface of an underlying insulator and made of at least one member selected from the group consisting of Ti, Ta, Mo, Cr, Nb and W and their alloy, a main conductor made of Cu formed in a predetermined pattern on the underlying conductor, a first coating conductor made of at least one member selected from the group consisting of Ti, Ta, Mo, Nb and Ni and their alloy, and a second coating conductor made of at least one member selected from the group consisting of Au and Al and their alloy that are formed in this order so as to coat a surface of the main conductor made of Cu facing the surrounding insulator.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electronic device having a layeredconductor wiring using Cu as a main conductor, and also relates to amagnetic device having a coil formed of a layered conductor wiring.

2. Description of the Related Art

Recently, there has been a rapid progress in light-weightminiaturization of various electronic apparatuses. There is a strongdemand for electronic devices constituting the electronic apparatuses tobe smaller, thinner, and lighter than ever before. To satisfy thedemands, a surface mounting device (SMD) is now widely employed.Furthermore, to integrate SMDs at a high density, studies have beenconducted on a multi-chip module (MCM) comprising a multi-layer wiringsubstrate and a plurality of bare chips mounted on the substrate.

In the multi-layer wiring substrate, it is required that the resistanceof the wiring and the dielectric constant of the insulating materialaround the wiring should be low in order to reduce a signal transmissiondelay. To satisfy this requirement, Cu is used as a wiring conductormaterial and SiO₂, polyimide, or the like is used as a surroundinginsulating material. If a structure is formed by contacting Cu directlywith the insulating material, Cu will be diffused into SiO₂ or reactedwith polyamic acid that is the precursor of the polyimide. Consequently,the dielectric constant of the insulating material decreases and furtherthe wiring resistance increases, in some cases. Generally, in the priorart, a multi-layer wiring is formed so as not to contact Cu directlywith the insulating material. For example, in the case where SiO₂ isused as the insulating material, Cu is coated with Ti or TiN to suppressCu diffusion. On the other hand, when polyimide is used as theinsulating material, Cu is coated with Ni or Ti to suppress the reactionbetween Cu and the precursor solution of the polyimide.

Now, we will explain an example of a manufacturing process of aconventional multi-layer wiring substrate using Cu as the main conductorand polyimide as an insulating material.

(a) First, on an insulating substrate made of, for example, alumina, aTi film and a Cu film are sequentially formed by a vacuum depositionmethod or the like. The Ti film used herein is approximately 0.1 μm inthickness and is used as an underlying conductor exhibiting goodadhesiveness to the substrate. The Cu film used herein is approximately1 μm in thickness and is utilized as a conductor for a plating electrodewhich will be part of the main conductor. Thereafter, a thick resistfilm is coated over the entire surface of the above-obtained structureand is patterned by photolithography, thereby forming openings at aportion in which wiring is formed.

(b) After Cu as the main conductor is allowed to grow by electroplatingin the opening portion of the resist to a predetermined thickness, theresist is peeled off. As a coating for suppressing the reaction betweenthe Cu main conductor and a polyimide precursor, a Ti film is formed bythe vacuum deposition method or the like so as to cover an exposed Cuface.

(c) A resist for removing a layered conductor (Ti/Cu/Ti) present in aspace portion is patterned by photolithography. Thereafter, using theresist thus patterned as a mask, Ti and Cu are alternately etched by anenchant for removing Ti containing mainly of acetic acid, nitric acidand hydrofluoric acid, and by an etchant for removing Cu containingferric chloride and water.

(d) A polyimide film serving as an insulator is formed over the entiresurface and contact holes are made therein.

(e) The aforementioned steps (a) to (d) are repeated, thereby forming amulti-layer wiring. Finally, pad holes are made, and an Ni film havingat least 1 μm in thickness and an Au film having at least 1 μm inthickness, both serving as a pad conductor, are sequentially formed bythe vacuum deposition method or the like. After that, a resist (notshown) is patterned by photolithography. Using the resist pattern as amask, Au and Ni present other than the pad portion are removed, therebyforming the pad conductor.

However, the aforementioned prior art has the following problems:

(1) It is difficult to control the alternate etching of Ti/Cu/Ti in Step(c) without failure. For example, when Cu is etched, a side etching ofCu is inevitable since Ti is scarcely etched. As a result, overhang ofTi occurs as shown in FIG. 1. If the overhang occurs in a lower portionof the conductor, air foams may be easily incorporated when a precursorof polyimide serving as an insulator is coated in a later step. Airfoams, if incorporated in a multi-layer wiring substrate, cause variousproblems.

(2) Fabrication steps are complicated since patterning has to beperformed after the pad portion is independently coated with a metalsuch as Ni or Au.

Of the aforementioned problems, it is considered that problem (2) can beovercome by coating the main conductor made of Cu with Al or an Al alloyas described in, for example, Jpn. Pat. Appln. KOKAI Publication No.60-128641. However, the Al or Al alloy coating Cu inducesstress-migration, thermal-migration, or electro-migration which mayfurther cause hillocks. The generated hillocks are likely to developinto a number of voids which possibly facilitate reaction of an exposedCu portion with an insulator.

Furthermore, the conductor material which is formed into a coil, is usedin an planar inductor or transformer, and a thin-film magnetic head. Inthis case, also, Cu having a high conductivity is mostly used to reducecoil resistance. Hitherto, in such magnetic devices, a resist is widelyused as an insulator between coil lines and of the upper portion of thecoil lines (Amorphous Electron Device Research Institute, ResearchReport, April, 1994). This is because when polyimide or SiO₂ is usedinstead of a resist as an insulator, the same problems are caused as inthe case of the multi-layer wiring substrate mentioned above, that is,difficulties associated with a process control and complexity ofmanufacturing steps. For example, in a thin-film magnetic head having aconductor consisting of Cu coated with Ni described in Jpn. Pat. Appln.KOKAI Publication No. 1-277311, the aforementioned problems areinevitably caused. When a resist is used as an insulator, due to poorthermal resistance of the resist, temperature of a process has to bereduced. In particular, when annealing is performed in the magneticfield to impart magnetic anisotropy to a magnetic substance, theuppermost temperature is restricted to a heat resistance temperature ofthe resist (approximately 200° C.). For this reason, it is impossible tosufficiently reduce magnetic anisotropic dispersion, causing problematicdeterioration in frequency characteristic.

As described above, in electronic devices such as a multi-layer wiringsubstrate containing a layered conductor wiring using Cu as the mainconductor, and in magnetic devices represented by an inductor,transformer and magnetic head, containing a planar coil formed of suchlayered conductor wiring, there are problems such as difficultiesassociated with a process control and complexity in manufacturing steps.Furthermore, since a process cost increases accompanying these problems,practical uses of the electronic devices and magnetic devices aredelayed. Hence, they have not yet risen large-scale industrial demands.

SUMMARY OF THE INVENTION

An object of the present invention is to improve controlling of aprocess and is to simplify manufacturing steps of a layered conductorwiring using Cu as the main conductor, thereby attaining a reduction ofcost and practical uses of the electronic devices such as a multi-layerwiring substrate and of the magnetic devices such as an inductor,transformer, and magnetic head, all using the layered conductor wiring.

The electronic device of the present invention comprises a conductorwiring enclosed with an underlying insulator and a surroundinginsulator, the conductor wiring having an underlying conductor formed ina predetermined pattern on a surface of the underlying insulator andmade of at least one selected from the group consisting of Ti, Ta, Mo,Cr, Nb, and W; a main conductor made of Cu formed on the underlyingconductor in a predetermined pattern; a first coating conductor made ofat least one selected from the group consisting of Ti, Ta, Mo, Nb, andNi and a second coating conductor made of at least one selected from thegroup consisting of Au and Al that are formed in this order so as tocoat the surface facing the surrounding insulator of the main conductormade of Cu.

The magnetic devices of the present invention are those which have acoil formed by using the layered conductor wiring having theaforementioned structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a conventional layeredconductor wiring;

FIG. 2 is a cross-sectional view showing an example of the layeredconductor wiring according to the present invention;

FIGS. 3A to 3C are cross-sectional views showing the layered conductorwiring according to the present invention;

FIGS. 4A to 4E are cross-sectional views showing an example of themanufacturing process of the layered conductor wiring according to thepresent invention;

FIGS. 5A to 5E are cross-sectional views showing another example of themanufacturing process of the layered conductor wiring according to thepresent invention;

FIGS. 6A to 6E are cross-sectional views showing still another exampleof the manufacturing process of the layered conductor wiring accordingto the present invention;

FIGS. 7A and 7B are a plan and cross-sectional views of the thin-filmcoil fabricated in Example 3 of the present invention;

FIGS. 8A and 8B are a plan and cross-sectional views of a planar chokecoil fabricated in Example 4 of the present invention;

FIG. 9 is a perspective view of the planar transformer fabricated inanother Example of the present invention; and

FIG. 10 is a perspective view of the thin-film magnetic head fabricatedin still another Example of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The layered conductor wiring according to the present invention is shownin FIG. 2. As shown in this figure, on an underlying insulator 1, anunderlying insulator 2 processed in a predetermined pattern and the mainconductor 3 made of Cu are formed. The surface facing a surroundinginsulator of the main conductor 3 made of Cu is coated with a firstcoating conductor 4 and a second coating conductor 5. The surroundinginsulator 6 made of polyimide or SiO₂ is provided on the layeredconductor wiring having such a structure. Furthermore, contact holes areformed in the insulator 6, and a bonding wire 10 made of Au or Al isconnected to the second coating conductor 5.

As described above, as the underlying conductor, use is made of at leastone type of metal selected from the group consisting of Ti, Ta, Mo, Cr,Nb, and W and their alloy. As the first coating conductor, use is madeof at least one type of metal selected from the group consisting of Ti,Ta, Mo, Nb, and Ni and their alloy. As the second coating conductor, useis made of at least one type of metal selected from the group consistingof Au and Al and their alloy.

The thickness of the underlying conductor 2 is preferably 0.05 μm ormore, the thickness of the first and second coating conductors 4 and 5is 0.5 μm or more, and preferably 1 μm or more. This is defined on thebasis of the following. That is, if the thickness of the underlyingconductor 2 is extremely thin, a failure in adhesion will occur due todiffusion of Cu. In contrast, if the thickness of the second coatingconductors 4 and 5 is extremely thin, sufficient mechanical strengthwill not be obtained when bonding wires are connected to pad portions.The uppermost thickness of the underlying conductor 2, the first andsecond coating conductors 4 and 5 may be set to a value thinner thanthat of the main conductor 3 made of Cu. The uppermost thickness,although varies depending on usage, is generally 10 μm or less.

In the layered wiring according to the present invention, by selectingan appropriate metal species from the metal group mentioned above as theunderlying conductor 2, the first and second coating conductors 4 and 5,no overhang are generated in the lower portion of a conductor wiring asshown in FIGS. 3A to 3C, although the conductor wiring is different inshape depending on a manufacturing process.

Cu as a main conductor is protected from SiO₂ or polyimide used as aninsulator between adjacent conductors or an interlayer conductor appliedin a multi-layer conductor, thereby suppressing Cu diffusion into SiO₂and a reaction of Cu with polyimide.

Furthermore, since the first coating conductor interposed between themain conductor made of Cu and the second coating conductor made of Al,Au or an Al-Au alloy is a metal having a high melting point, the metalitself rarely causes migration, with the result that hillocks developinginto voids are not generated. Owing to this, Cu will not be exposed andthe conductor wiring using Cu as the main conductor will be improved inreliability.

Since the first coating conductor positioned in the lower portion of thesecond coating conductor (Al or/and Au) is a hard material, even if thesecond coating conductor, which is exposed by forming contact holes inthe insulator 6 on the wiring, is used as a pad portion, and a bondingwire made of Al or Au is directly wedge-bonded or ball-bonded thereto,sufficient mechanical strength will be maintained. Accordingly, a stepof depositing a metal onto a pad portion and patterning it, is no longernecessary, thereby shortening manufacturing steps.

In the layered conductor wiring according to the present invention, themain conductor made of Cu, the underlying conductor (hereinafter,referred to as "Metal A"), the first coating conductor (hereinafter,referred to as "Metal B") and the second coating conductor (hereinafter,referred to as "Metal C") may be formed by the vacuum deposition,sputtering method, or the like. Alternatively, thick Cu film may beformed as the main conductor by electroplating using a previously-formedCu film as an electrode. The manufacturing process will be morespecifically explained with reference to FIGS. 4A to 4E, FIGS. 5A to 5E,and FIGS. 6A to 6E.

FIGS. 4A to 4E show an example of the manufacturing steps in the casewhere Cu as the main conductor is formed into a thin film of less than10 μm in thickness by the vacuum deposition or the sputtering method.First, on an insulating substrate 1, an underlying conductor 2 made ofMetal A, which strengthens the adhesiveness to the substrate, and a mainconductor 3 made of Cu are formed. Upon the structure thus obtained, aphotoresist 21 is formed in a predetermined pattern (FIG. 4A).Subsequently, using the photoresist 21 as a mask, Cu and Metal A areetched together with an etchant (FIG. 4B). Thereafter, over the entiresurface of the above-obtained structure, a first coating conductor 4made of Metal B and a second coating conductor 5 made of Metal C aresequentially formed (FIG. 4C). After that, a photoresist 22 is formed ina predetermined pattern so as to cover the main conductor line byphotolithography (FIG. 4D). Then, using the photoresist 22 as a mask,Metals C and B present in the area other than the main conductor lineare etched together (FIG. 4E).

In this method, Metal A and the etchant 1 used in the step of FIG. 4Bshould be chosen in such a way that the relationship of etching rates inthe etchant 1 satisfy the following condition:

    R.sub.1.Cu ≧R.sub.1.A                               (1)

Metals C, B and the etchant 2 used in the step of FIG. 4E should bechosen in such way that the relationship of etching rates in the etchant2 satisfy the following condition:

    R.sub.2.C ≧R.sub.2.B                                (2)

In this way, by choosing an appropriate metal species and an etchant,the lower portion of the wiring may be formed as shown in FIG. 3A andoverhang will not be generated.

FIGS. 5A to 5E show an example of the manufacturing steps in the casewhere the main Conductor made of Cu is formed into a thick film of 10 μmor more in thickness by electroplating. First, on an insulatingsubstrate 1, an underlying conductor 2 made of Metal A, whichstrengthens the adhesiveness to the substrate, and a conductor 3a for aplating electrode made of Cu which will be part of the main conductor,are formed. On the structure thus obtained, a photoresist 23 is formedin a predetermined pattern (FIG. 5A). Subsequently, using an appropriateplating solution, the main conductor made of Cu is allowed to grow onthe conductor 3a for a plating electrode which exposed from aphotoresist 23 and then the photoresist 23 is removed (FIG. 5B).Subsequently, over the entire surface of the above-obtained structure, afirst coating conductor 4 made of Metal B and a second coating conductor5 made of Metal C are sequentially formed (FIG. 5C). After that, aphotoresist 24 is formed by photolithography in a predetermined patternso as to cover the main conductor line (FIG. 5D). Further, using thephotoresist 24 as a mask, Metals C and B, Cu and Metal A present in thearea other than the main conductor line are etched together with anetchant (FIG. 5E).

In this method, Metals C, B, A and the etchant used in the step of FIG.5E should be chosen in such a way that the relationship of etching ratesin the etchant satisfy the following condition:

    R.sub.C ≧R.sub.B ≧R.sub.Cu ≧R.sub.A   (3)

In this way, by choosing an appropriate metal species and an etchant,the lower portion of the wiring may be formed as shown in FIG. 3B andoverhang will not be generated.

FIGS. 6A to 6E show an example of the manufacturing steps usingelectroplating. First, on an insulating substrate 1, an underlyingconductor 2 made of Metal A and a conductor 3a for a plating electrodemade of Cu which will be part of the main conductor are formed in thesame manners as in FIG. 5A. Further, on the above-obtained structure, aphotoresist is formed in a predetermined pattern and the main conductor3 made of Cu is allowed to grow by electroplating and then thephotoresist is removed in the same manners as in FIG. 5B.

Subsequently, a photoresist 25 is formed in a predetermined pattern soas to cover the main conductor line (FIG. 6A). Thereafter, using thephotoresist 25 as a mask, Cu and Metal A are etched together with anetchant (FIG. 6B). Then, over the entire surface, a first coatingconductor 4 made of Metal B and a second coating conductor 5 made ofMetal C are sequentially formed (FIG. 6C). After that, a photoresist 26is formed by photolithography in a predetermined pattern so as to coverthe main conductor line (FIG. 6D). Then, using the photoresist 26 as amask, Metals C and B present in the area other than the main conductorline are etched together with an etchant (FIG. 6E).

Also in this method, Metal A and the etchant 1 used in the step of FIG.6B should be chosen in such a way that the relationship of etching ratesin the etchant 1 satisfy the condition given by aforementioned formula(1). Metals C, B and the etchant 2 used in the step of FIG. 6E should bechosen in such a way that the relationship of etching rates in theetchant 2 satisfy the condition given by the aforementioned formula (2).

In this way, by choosing an appropriate metal species and an etchant,the lower portion of the wiring may be formed as shown in FIG. 3C andoverhang will not be generated.

A combination of a metal and an etchant satisfying the conditions givenby formulas (1) to (3) may be uncountable. By way of reference ofchoosing a metal and an etchant satisfying predetermined conditions, therelative etching abilities of various types of metal elements to variousetchants are listed in Table 1. With respect to a given etchant shown inTable 1, a metal susceptible to etching at room temperature is indicatedas ⊚; a metal susceptible to etching at 100° C. is indicated as ◯; and ametal insusceptible to etching is indicated as "x". Under predeterminedetching conditions, the etching rate gets slower in sequential order of⊚ to "x". Hence, with reference to this Table, the metal and etchant tobe chosen can be determined.

                  TABLE 1                                                         ______________________________________                                        Main Metal elements and Etchants                                                           Metal elements                                                   Etchant        Al    Ti    Ta  Cr  Mo  W   Ni  Cu  Au                         ______________________________________                                        HF             ⊚                                                                    ⊚                                                                    ⊚                                                                  X   X   X   X   X   X                          HCl (dil.)     ⊚                                                                    ◯                                                                       X   ⊚                                                                  X   X   ◯                                                                     X   X                          HCl (conc)     ⊚                                                                    ⊚                                                                    X   ⊚                                                                  X   X   ⊚                                                                  ◯                                                                     X                          HNO.sub.3 (dil.)                                                                             ◯                                                                       X     X   X   ⊚                                                                  X   ⊚                                                                  ⊚                                                                  X                          HNO.sub.3 (conc)                                                                             ◯                                                                       X     X   X   ◯                                                                     X   X   ⊚                                                                  X                          HClO.sub.3 (dil.)                                                                            ◯                                                                       X     X   X   ⊚                                                                  X   ⊚                                                                  ⊚                                                                  X                          HClO.sub.3 (conc)                                                                            ◯                                                                       X     X   X   ◯                                                                     X   X   ⊚                                                                  X                          H.sub.2 SO.sub.4 (dil.)                                                                      ⊚                                                                    ◯                                                                       X   ⊚                                                                  X   X   ⊚                                                                  X   X                          H.sub.2 SO.sub.4 (conc)                                                                      ⊚                                                                    ⊚                                                                    --  ⊚                                                                  ◯                                                                     --  ⊚                                                                  ⊚                                                                  X                          H.sub.3 PO.sub.4 (dil.)                                                                      ◯                                                                       ◯                                                                       X   X   X   X   ⊚                                                                  X   X                          H.sub.3 PO.sub.4 (conc)                                                                      ⊚                                                                    ⊚                                                                    X   X   X   X   ⊚                                                                  ◯                                                                     X                          H.sub.2 C.sub.2 O.sub.4                                                                      ⊚                                                                    ◯                                                                       X   X   X   X   ⊚                                                                  X   X                          HNO.sub.3 (conc) + HCl (conc)                                                                ⊚                                                                    X     X   ◯                                                                     ⊚                                                                  ◯                                                                     ⊚                                                                  ⊚                                                                  ⊚           NHO.sub.3 (conc) + HF                                                                        ⊚                                                                    ⊚                                                                    ⊚                                                                  ⊚                                                                  ⊚                                                                  ⊚                                                                  ⊚                                                                  ⊚                                                                  X                          CrO.sub.3 + H.sub.2 SO.sub.4                                                                 ⊚                                                                    X     X   X   X   X   X   ⊚                                                                  X                          FeCl.sub.3     ⊚                                                                    X     X   ⊚                                                                  ⊚                                                                  X   ⊚                                                                  ⊚                                                                  X                          SnCl.sub.2     ⊚                                                                    X     X   ⊚                                                                  X   X   ⊚                                                                  X   X                          HgCl.sub.2     ⊚                                                                    X     X   ⊚                                                                  X   X   ⊚                                                                  ⊚                                                                  X                          KOH(dil.)      ⊚                                                                    X     X   X   X   X   X   X   X                          KOH(conc)      ⊚                                                                    X     ⊚                                                                  X   X   X   X   ⊚                                                                  X                          K.sub.3 Fe(CN).sub.6 + KOH                                                                   ⊚                                                                    X     ◯                                                                     ⊚                                                                  ⊚                                                                  ⊚                                                                  --  ⊚                                                                  X                          KI + I.sub.2   ⊚                                                                    X     X   --  X   X   ◯                                                                     ⊚                                                                  ⊚           ______________________________________                                         ⊚; Susceptible to etching at room temperature                  ◯; Susceptible to etching at 100° C.                       X; nonsusceptible to etching                                                  --; no data                                                              

EXAMPLES

Hereinbelow, Examples of the present invention will be explained withreference to Figures.

Example 1

In accordance with manufacturing steps shown in FIGS. 4A to 4E, alayered conductor wiring is manufactured.

First, on the surface of an alumina substrate, a 0.1 μm-thick Mo film asan underlying conductor and a 5 μm-thick Cu film as the main conductorare sequentially formed by the vacuum deposition method. Thereafter, aphotoresist pattern corresponding to a circuit pattern is formed byphotolithography. Subsequently, using this photoresist pattern as a maskand a mixed solution consisting of phosphoric acid (77 vol %), nitricacid (3 vol %), acetic acid (15 vol %) and water (5 vol %) as anetchant, the 5 μm-thick Cu film and the 0.1 μm-thick Mo film are etchedtogether. The etching rate of Cu herein is approximately 0.4 μm/min, andthat of Mo is approximately 0.1 μm/min.

Second, over the entire surface, a 1 μm-thick Mo film as a first coatingconductor and a 1 μm-thick Al film as a second coating conductor aresequentially formed by the vacuum deposition method. Subsequently, aphotoresist pattern is formed so as to enclose the Cu/Mo wiring line.Using this photoresist pattern as a mask, and a mixed solution ofphosphoric acid (95.4 vol %), nitric acid (0.6 vol %), acetic acid (3.0vol %) and water (1.0 vol %) as an etchant, the 1 μm-thick Mo film andthe 1 μm-thick Al film are etched together. The etching rate of Moherein is approximately 0.05 μm/min, and that of Al is approximately0.08 μm/min. Through these steps, a layered conductor wiring issuccessfully formed, with no overhang in the lower portion as shown inFIG. 3A.

Thereafter, polyamic acid as a polyimide precursor is spin-coated ontothe entire surface so as not to incorporate air foams therein underreduced pressure, in an atmosphere of, its solvent, followed by curingat 350° C. for 120 minutes. On the polyimide insulator thus cured, aphotoresist pattern for use in making contact holes is formed. Usingthis photoresist as a mask, chemical dry etching (CDE) using mixed gasof oxygen and carbon tetrafluoride is applied to the polyimide to formcontact holes. Furthermore, on the thus obtained structure, layeredconductor wirings constituting the second layers or above aresequentially formed, thereby preparing a multi-layer wiring substrate.

Example 2

In accordance with manufacturing steps shown in FIGS. 6A to 6E, alayered conductor wiring is manufactured as follows:

First, on a silicon substrate having a 0.2 μm-thick thermal oxide filmon the surface thereof, a 0.1 μm-thick Mo film as an underlyingconductor and a 1 μm-thick Cu film as a plating electrode conductor aresubsequently formed by a DC magnetron sputtering method. After aphotoresist pattern corresponding to a reversal pattern of a circuitpattern is formed by photolithography, Cu serving as the main conductoris electroplating onto the Cu film to 40 μm in thickness at a currentdensity of 15 mA/cm², using a solution containing mainly sulfuric acid,copper sulfate, and hydrochloric acid. Thereafter, the resist is removedwith acetone and the resultant structure is washed in pure water. Sincethe plated conductor has a reverse tapered form having an angle of 80°,if the resist pattern, whose width is slightly narrower than that of theplated conductor, is formed on the plated Cu conductor line as a maskand etching is performed with an etchant, i.e., a mixed solution ofphosphoric acid (77 vol %), nitric acid (3 vol %), acetic acid (15 vol%) and water (5 vol %), excessive Cu can be removed. As a result, thewidth of the plated conductor line is slightly reduced but the reversetapered portions almost disappear. At this time, simultaneously the Cufilm is slightly etched away from the area (space portions) other thanthe lines. The Cu etching rate herein is 0.4 μm/min.

Thereafter, a photoresist pattern is formed so as to enclose the platedCu conductor line. Using the photoresist pattern as a mask and a mixedsolution of phosphoric acid (77 vol %), nitric acid (3 vol %), aceticacid (15 vol %) and water (5 vol %) as an etchant, the Cu film and Mofilm of the space portions are etched away together. The Cu etching rateherein is 0.4 μm/min, and the Mo etching rate is 0.1 μm/min.

Subsequently, over the entire surface, 1 μm-thick Mo film as a firstcoating conductor and 1 μm-thick Al film as a second coating conductorare subsequently formed by the DC magnetron sputtering method. At thistime, the Mo and Al films are formed under suitable conditions that agood step coverage is established, for example, under a raised Ar gaspressure, thereby coating a side wall of the 40 μm-thick Cu conductorwith the Mo and Al films of 0.5 μm or more in thickness. After that, aphotoresist pattern is formed so as to enclose the conductor line. Usingthe photoresist pattern as a mask, and a mixed solution of phosphoricacid (95.4 vol %), nitric acid (0.6 vol %), acetic acid (3.0 vol %) andwater (1.0 vol %) as an etchant, the 1 μm-thick Mo film and 1 μm-thickAl film are etched away together. The Mo etching rate herein isapproximately 0.05 μm/min and the Al etching rate is approximately 0.08μm/min.

Through these steps, a thick-film layered conductor wiring can be formedwith no overhang in the lower portion as shown in FIG. 3C.

Subsequently, polyimide is formed in the same manner as in Example 1 andcontact holes are made by chemical dry etching. Furthermore, on theabove-obtained structure, layered conductor wirings constituting circuitpatterns of the second layer or above are sequentially formed, therebyforming a multi-layer thick-film wiring substrate.

Example 3

A planar thin-film coil shown in FIGS. 7A and 7B is manufactured inaccordance with the steps of the Example 1. FIG. 7A is a plan view andFIG. 7B is a cross-sectional view. In FIGS. 7A and 7B, on an aluminasubstrate 31, a planar coil 32 consisting of a mono-layered conductorwiring having a structure shown in FIG. 3A. The planar thin-film coilhas a square spiral pattern with a number of turns of 5. The line andspace of the layered conductor are 20 μm in width, an outer size of thesquare spiral coil is 500 μm. Subsequently, an SiO₂ film 33 serving asan insulating film between conductor lines and a protection film iscoated over the entire surface by the plasma CVD method. Thereafter,using a resist as a mask, pad portions 34 are made by the RIE methodusing carbon tetrafluoride as reaction gas. Thereby an Al surface isexposed.

The coil functions normally as a direct current choke for a poweramplifier used in an 800 MHz analog mobile phone.

Example 4

A planar choke coil for an MHz switching power source, shown in FIGS. 8Aand 8B, is manufactured in accordance with the steps of Example 2. FIG.8A is a plan view and FIG. 8B is a cross-sectional view. In FIGS. 8A and8B, on a silicon substrate 40 having a thermal oxide film 41 on thesurface thereof, a lower magnetic thin film 42, an SiO₂ film 43, a coil44, a polyimide film 45, an upper magnetic thin film 46, and a polyimidefilm 47 are subsequently formed. The coil 44 is sandwiched between theupper magnetic thin film 46 and the lower magnetic thin film 42. In thischoke coil, uniaxial magnetic anisotropy is imparted to the magneticthin films, of which easy axis of magnetization is indicated by an arrowin FIG. 8A, so that the magnetic thin films are excited in the directionof the hard axis of magnetization in almost all area of the device.

Hereinafter, a manufacturing process of the choke coil will be explainedin detail. On a silicon substrate 40 having a thermal oxide film 41formed thereon, 0.1 μm-thick Al, AlN_(x) (x=0-0.5) and AlN_(x) (x=0.5-1)films (not shown) are sequentially formed to improve adhesiveness of thelower magnetic thin film. On the AlN_(x) (x=0.5-1) film, a 6.0 μm-thicklower magnetic thin film 42 is formed. The magnetic thin film 42 is ofFeCoBC-based and hetero amorphous magnetic film in which an amorphousmagnetic phase rich in FeCo and an amorphous insulating phase rich inboron and carbon are homogeneously dispersed. The saturation magneticflux density of the film 42 is 1.6 T, the relative magnetic permeabilityin the direction of the hard axis of magnetization is 1100, andresistivity is 300 μΩ·cm. Using a resist pattern as a mask and a mixedsolution of phosphoric acid (77 vol %), nitric acid (3 vol. %), aceticacid (15 vol %) and water (5 vol %) as an etchant, the magnetic thinfilm is etched. On this structure, 5.0 μm-thick SiO₂ film 43 is formedby sputtering. On the film 43, a coil 44 consisting of a layeredconductor having a cross-sectional structure shown in FIG. 3C is formedin the same manner as in Example 2. The coil 44 has a pattern in whichtwo rectangular spiral coils, one is a right handed spiral, the other isa left handed spiral, are juxtaposed to each other. The number of turnsof the coil is 6. The thickness of the Cu conductor is 50 μm.Subsequently, a polyimide film 45 is formed between lines of the coil 44and on the lines in the same manner as in Example 1. After the surfaceof the polyimide film 45 is sufficiently made flat, a 6 μm-thick uppermagnetic thin film 46 is formed of the same material as that employed inthe lower magnetic thin film 42 and etched in the same manner as in thecase of the lower magnetic thin film 42. Further, over the film 46, apolyimide film 47 is formed as a protecting film. Subsequently, a resistpattern is formed in order to make holes in pad portions. Using theresist pattern as a mask, the polyimide film 47 is etched by chemicaldry etching using mixture gas of oxygen and carbon tetrafluoride andthereby the Al surface of the pad portion is exposed. Finally, a directcurrent magnetic field of 4 kA/m is applied to the magnetic thin filmsin the direction of an arrow shown in FIG. 8A in vacuum and then thefilms are subjected to heat treatment at 320° C. to impart uniaxialmagnetic anisotropy. Alternatively, the uniaxial magnetic anisotropy canbe imparted by forming a soft magnetic thin film in a direct currentmagnetic field.

The planar choke coil thus obtained has an inductance of 0.5 μH and adirect current coil resistance of 0.2 Ω. Further, a direct current atwhich the inductance reduces by 50% is 1.5 A.

A control IC, MOSFET for switching, and a Schottoky diode forrectification, all are bear chips, and the choke coil are bonded to eachother with an Au wire of 50 μm in diameter, thereby forming a boostchopper type DC to DC converter functioning at 5 MHz. This converter iscapable of raising a 3.6 V input voltage to 5.0 V and its powerconversion efficiency is 82% at the time when 3.0 W of power is output.

Other than the aforementioned Examples, various electronic devices andmagnetic devices can be manufactured by applying the present inventionas described follows:

For example, in accordance with the same manufacturing process of thelayered conductor wiring as in Example 2, a planar transformer can beformed, which has a primary and secondary layered conductor coils woundaround a magnetic thin film as shown in FIG. 9. In FIG. 9, on a siliconsubstrate 50 having a thermal oxide film 51 formed thereon, the lowerconductor of a primary coil 52, the lower conductor of a secondary coil53, a magnetic substance 54, the upper conductor of the primary coil 52and the upper conductor of the secondary coil 53, each independentlyinsulated, are layered. The lower conductor and upper conductorconstituting each coil are formed in a predetermined pattern in the samemanner as in Example 2 and connected to each other. The entire surfaceof the transformer is coated with a polyimide film 55. Pad holes aremade at portions of the surface corresponding to both ends of theprimary coil 52 and secondary coil 53.

Furthermore, a thin-film magnetic head for a hard disk drive as shown inFIG. 10 can be manufactured. In FIG. 10, on a silicon substrate 60having a thermal oxide film 61 formed thereon, SiO₂ film 63 having an MRsensor 64 embedded therein, the lower core 65 made of CoZrNb amorphoussoft magnetic thin film, SiO₂ film 66 which forms a 0.1 μm recording gapat the end of the head, a layered conductor coil 67 formed in the samemanner as in Example 2, a polyimide film 68 coated on the layeredconductor coil 67, and an upper core 69 made of 2.0 μm-thick CoZrNbamorphous soft magnetic thin film are subsequently formed.

Furthermore, other than Examples mentioned above, the layered conductorwiring of the present invention can be used in a wiring of asemiconductor device.

What is claimed is:
 1. An electronic device having a conductor wiring enclosed with an underlying insulator and a surrounding insulator,wherein said conductor wiring comprises an underlying conductor formed in a pattern on a surface of the underlying insulator, the underlying conductor made of at least one material selected from the group consisting of Ti, Ta, Mo, Cr, Nb, and W and their alloy; a main conductor made of Cu formed in a pattern on said underlying conductor; a first coating conductor made of at least one material selected from the group consisting of Ti, Ta, Mo, Nb, and Ni and their alloy, and a second coating conductor made of at least one material selected from the group consisting of Au and Al and their alloy that are formed in this order so as to coat a surface of said main conductor made of Cu facing the surrounding insulator.
 2. The electronic device according to claim 1, wherein said underlying conductor has a thickness of 0.05 to 10 μm.
 3. The electronic device according to claim 1, wherein said first and second coating conductors have a thickness of 0.5 to 10 μm.
 4. The electronic device according to claim 3, wherein said first and second coating conductors have a thickness of 1 to 10 μm.
 5. The electronic device according to claim 1, wherein when said main conductor made of Cu and underlying conductor are simultaneously etched with a first etchant, if etching rates of said main conductor and underlying conductor are defined as R₁.Cu and R₁.A, respectively, said etching rates should satisfy the following relationship:

    R.sub.1.Cu ≧R.sub.1.A,

and when said first and second coating conductors are simultaneously etched with a second etchant, if etching rates of said first and second coating conductors are defined as R₂.B and R₂.C, respectively, said etching rates should satisfy the following relationship:

    R.sub.2.C ≧R.sub.2.B.


6. The electric device according to claim 1, wherein when said main conductor made of Cu, said underlying conductor, and said first and second coating conductors are simultaneously etched with an etchant, if etching rates of said main conductor, underlying conductor and first and second coating conductors are defined as R_(Cu), R_(A), R_(B) and R_(C), respectively, said etchings rates should satisfy the following relationship:

    R.sub.C ≧R.sub.B ≧R.sub.Cu ≧R.sub.A.


7. The electronic device according to claim 1, further comprising:a second conductor wiring formed on the surface of the surrounding insulator, wherein the second conductor wiring comprises: a second underlying conductor formed in a pattern on a surface of the surrounding insulator, the second underlying conductor made of at least one material selected from the group consisting of Ti, Ta, Mo, Cr, Nb, and W and their alloy; a second main conductor made of Cu formed in a pattern on said second underlying conductor; a third coating conductor made of at least one material selected from the group consisting of Ti, Ta, Mo, Nb, and Ni and their alloy, and a fourth coating conductor made of at least one material selected from the group consisting of Au and Al and their alloy that are formed in this order so as to coat a surface of said second main conductor; and a second surrounding insulator disposed about the second conductor wiring.
 8. A magnetic device having a coil made of a conductor enclosed with an underlying insulator and a surrounding insulator,wherein said coil comprises an underlying conductor formed in a pattern on a surface of the underlying insulator, the underlying conductor made of at least one material selected from the group consisting of Ti, Ta, Mo, Cr, Nb, and W and their alloy; a main conductor made of Cu formed in a pattern on said underlying conductor; a first coating conductor made of at least one material selected from the group consisting of Ti, Ta, Mo, Nb, and Ni and their alloy, and a second coating conductor made of at least one material selected from the group consisting of Au and Al and their alloy that are formed in this order so as to coat a surface of said main conductor made of Cu facing the surrounding insulator.
 9. The magnetic device according to claim 8, wherein said underlying conductor has a thickness of 0.05 to 10 μm.
 10. The magnetic device according to claim 8, wherein said first and second coating conductors have a thickness of 0.5 to 10 μm.
 11. The magnetic device according to claim 10, wherein said first and second coating conductors have thickness of 1 to 10 μm.
 12. The magnetic device according to claim 8, wherein when said main conductor made of Cu and said underlying conductor are simultaneously etched with a first etchant, if etching rates of said main conductor and underlying conductor are defined as R₁.Cu and R₁.A, respectively, said etching rates should satisfy the following relationship:

    R.sub.1.Cu ≧R.sub.1.A,

and when said first and second coating conductors are simultaneously etched with a second etchant, if etching rates of said first and second coating conductors are defined as R₂.B and R₂.C, respectively, said etching rates should satisfy the following relationship:

    R.sub.2.C ≧R.sub.2.B.


13. The magnetic device according to claim 8, wherein when said main conductor made of Cu, said underlying conductor, and said first and second conductors are simultaneously etched with an etchant, if etching rates of said main conductor, said underlying conductor and said first and second conductors are defined as R_(Cu), R_(A), R_(B) and R_(C), respectively, said etching rates should satisfy the following relationship:

    R.sub.C ≧R.sub.B ≧R.sub.Cu ≧R.sub.A.


14. The magnetic device according to claim 8, wherein said coil has a planar form. 